The present invention relates to a moisture-responsive valve assembly for controlling the flow of a liquid in response to moisture. The invention is particularly applicable as a moisture-responsive valve in a water irrigation system for controlling the flow of the irrigation water to the irrigating devices, such as drip-irrigation emitters, in response to the moisture content of the soil; therefore, the invention is described below with respect to this application.
In the conventional water-irrigation system, all the irrigating devices for a particular plot of land are generally turned on for a specified time period, or after a specified quantity of water has been dispensed, and then all are turned off. Such a system tends to supply the same quantity of water to all the irrigating devices, irrespective of the moisture content of the soil at the individual locations of the irrigating devices. This results in a wastage of water since some locations receive more water than required particularly if the system is designed so that no location receives less water than required. Moreover, such systems require either manual control for turning-on and turning-off the water irrigation devices according to the desired time intervals or quantities of water dispensed, or automatic control equipment for performing these functions.
A number of moisture-responsive valves have been developed for controlling the water supplied to the irrigating devices in response to the moisture content of the soil. In most of such known systems, however, the moisture-responsive valve may partially open and assume a stable state of remaining partially open by the continuous discharge of a small quantity of water, thereby disabling it from its normal control function. In one known device as illustrated in U.S. Pat. No. 3,747,399, the valve opens with a snap-action, but does not close with a snap-action, and therefore the valve in that device may also remain in a partially-open position. Moreover, such a device, as well as many of the other known devices, are of relatively complicated structures which are costly to produce and to maintain.